Industrial Robot

Background

Industrial robots are mechanical devices which, to a certain degree,
replicate human motions. They are used whenever there is a need to reduce
the danger to a human, provide more strength or accuracy than a human, or
when continuous operation is required. Most robots are stationary, but
some move throughout the workplace delivering materials and supplies.

Many people think of robots as the humanoid-type monsters that are seen in
science fiction and fantasy movies. While we may someday have the
technical ability to produce such a machine, today's robots are
actually quite simple devices. Motions that we take for
granted—picking up a coin from the table, for instance—are
considerably more difficult for a robot. Our brain processes thousands of
variable bits of data from our eyes to instruct our arm, wrist, hand, and
fingers to reach, grasp, and pick up the
coin.
Even the tactile feel of the coin constantly updates our brain to provide
just enough finger pressure to grip the coin securely. Any variations in
position are effortlessly compensated for in our brain. To easily and
economically program an industrial robot to perform the same task, many of
these variables must be restricted or eliminated. Position, reach, weight,
and grasp should remain as consistent as possible so that variations do
not result in missing or dropping the object. The computer that controls
the robot must be programmed by a technician, to "teach" the
machine to complete the motion. The areas where robots perform better than
humans are in accuracy and repeatability. While some people could pick up
the coin with similar motions each time, the robot can perform the
operation with exactly the same motions without tiring. Many robots can
repeat motions with an accuracy of a few thousandths of an inch and
operate 24 hours a day. Because of this tireless, accurate work, robots
are a growing segment of industrial equipment purchases. Most are used for
repetitive painting and welding operations, while others, known as
pick-and-place robots, are used to lift and place products into machines
and packages.

History

Robots, or "robotics," are a segment of the broader science
of automation. Automation uses machines and computers which can learn or
compensate for varying conditions of operation. The term robot can be
traced to the Czech word
robota,
which means compulsory labor. The term first appeared in 1921 in the play
"R.U.R." (Rossum's Universal Robots) by Czech
dramatist Karel Capek. The play described humanoid robots that destroyed
their human makers—much the same plot of some modern science
fiction thrillers.

Practical robots were first attempted after the development of the
computer. In the late 1960s, the Stanford Research Institute designed and
built an experimental robot called "SHAKEY." Using a
television camera and a computer, this machine was capable of moving and
arranging blocks into stacks. General Motors financed a program at the
Massachusetts Institute of Technology in the mid-1970s to develop an
automated robot for assembly purposes. Here, researcher Victor Scheinman
invented the
PUMA (programmable universal manipulator for assembly), and the entry of
robots into American industry began.

Raw Materials

Robots are mostly built of common materials. Some specialized robots for
clean room applications, the space program, or other "high
tech" projects may use titanium metal and structural composites of
carbon fibers. The operating environment and strength required are major
factors in material selection.

Steel, cast
iron,
and aluminum are most often used for the arms and bases of robots. If the
robot is mobile, they usually equip them with rubber tires for quiet
operation and a positive grip on the floor. Robots contain a significant
amount of electronics and wiring, and some are radio or laser controlled.
The cylinders and other motion-generating mechanisms contain hydraulic oil
or pressurized air. Hoses of silicone, rubber, and braided stainless steel
connect these mechanisms to their control valves. To protect the robot
from the environment, some exposed areas are covered with flexible
neoprene shields and collapsible bellows. Electric motors and linear
drives are purchased from automation suppliers along with the controller,
or "brain." Controllers are housed in steel electrical
cabinets located near the robot's work area or carried on board the
robot itself.

The Manufacturing
Process

Design

1 Every robot begins with the design phase. These and other factors must
be accounted for in the design: job to be performed; speed of operation;
environment of operation; hazardous materials involved; length of reach;
path of travel; process variables; human involvement; controller
capability; and result of failures.

Most manufacturers have a basic machine design to which they
incorporate modifications and accessories to meet the specific
requirements of the application.

The first robot installed in American industry, this Unimate
"pick-and-place" uni) first removed hot metal parts
from a die-casting machine at a GM plant in Trenton, New Jersey,
in 1961.

(From the collections of Henry Ford Museum & Greenfield
Village.)

Robots, like any tool, are only as good as the people wielding them.
They cannot do jobs they were not designed or programmed to do. They are
most effective when the overall system and processes are carefully
planned. In addition, workers responsible for them have to be fully
educated and trained as well.

In the 1980s, the General Motors Corporation spent upwards of $40
billion on new technologies, many hundreds of millions on robots.
Unfortunately, the company did not spend nearly enough on understanding
the systems and processes that the robots were supposed to revolutionize
or on the people who were to maintain and operate them. The GM plant in
Hamtramck, Michigan, was supposed to be a showcase for the company.
Instead, by 1988 it was the site of some of the worst in technological
utopianism. Robots on the line sometimes painted each other rather than
the car bodies passing by; robots occasionally went out of control and
smashed into the passing vehicles; a robot designed to install
windshields was found systematically smashing them. Once, when a robot
ceased working, technicians did not know how to fix it. A hurried call
to the manufacturer brought a technician on the next plane. He looked at
the robot, pushed the "Reset" button, and the machine was
once again operational.

William S. Pretzer

Fabrication

2 Once designed, the base, arms, column, and supports are fabricated.
The base is

usually heavy, to prevent the robot from tipping over. It is made by
casting or by welding, then machined. Many robot manufacturers use
robots to weld parts for new ones.

Those areas that mate with the rest of the robot are machined with
close dimensional control to assure proper fit and operation of the
attaching components. Likewise, the main column and arms are
constructed to fit accurately into the final assembly.

Assembly

Robots are assembled using a substantial amount of purchased components
such as electric motors, hydraulic cylinders, bearings, wiring,
controllers, and other important parts. An industrial robot can contain
2,000 individual parts and is assembled by teams. These teams begin with
the base, and assemble components into the robot until it is complete and
ready for testing and finishing.

To begin the assembly process, mobile robots first have the traction
motors, batteries, axles, wheels, and tires mounted. Stationary robots do
not require these items. They are temporarily bolted to the floor for
stability during assembly. The moving columns and arms are subassembled
with their respective drive motors and then attached to the base. The base
contains a ring gear that is motor driven to provide the turning motion.
It must mate closely with the drive gear contained in the column. Thrust
bearings support the weight of column and arms on the base. A magnetic
scale surrounds the bearing and provides electronic position feedback to
the controller.

Link

3 The next joint is the link. It acts like an elbow, and connects the
arm to the base. A stabilizer support provides positional control to the
link, allowing it to move in a predetermined path. These components
contain bearing mounts into which pivot shafts are bolted. Each bearing
is prelubricated or provided with a lubrication line or fitting. The
link contains a position sensor which provides another position signal
to the controller.

Arm

4 The arm is assembled onto the upright portion of the link. It provides
the most "reach" to the robot and supports the wrist. The
arm contains the drive shafts that operate the wrist. Three motors, or a
combination of motors and hydraulic cylinders, are

An industrial robot can contain 2,000 individual parts and is
assembled by teams. These teams begin with the base, and assemble
components into the robot until it is complete and ready for testing
and finishing.

connected to the drive shafts. Since the arm and link joint must
withstand the entire load of the wrist, this is accomplished with large
bearings and a pivot pin.

Wrist

5 The wrist is the critical mechanism of the robot. It is the wrist that
most replicates human motion by twisting and turning to place the paint
gun, welder, or other tool in the correct position. Many robots also
have load-sensing electronics in the wrist to signal when an obstruction
has been hit, or when a load is too heavy to safely pick up. Additional
position sensors and tool control electronics are also assembled into
the arm and wrist.

Wiring to the controller

6 Once the mechanical assembly has been completed, the wiring and
plumbing of the robot can be finished. All of the

motor's sensors and electrical components must have wires for
power and to carry information back to the control computer.
Occasionally, unused space in the arms and base provides a handy place
to mount some of the controller electronics, shortening the wiring
paths. Hydraulic and air cylinders have hoses that carry pressure to
operate them, controlled from the valves in the base. Most of these
wires and hoses are routed back to the controller cabinet which, for
mobile robots, is attached to the base. If the robot is stationary, this
controller is usually mounted several feet away and is connected by an
umbilical cord. After assembly, the arms and column of the robot are
sometimes covered with guards and shields to protect them from paint
spray, welding sparks, or other hazards in the environment.

Installation

Installation occurs at the user's site. If / stationary, the robot
is secured to the floor with bolts. If moving, a guide wire is buried into
the floor for the robot to follow from task to task. It follows the wire
by radio signals and also uses the wire to communicate with the central
controller. Recently, lasers have been used to eliminate the wire. The
robot is guided through its path by a laser beam reflected off the walls.
Some designs also incorporate video cameras. Stationary applications
usually require that fences be constructed around the robot so an
unsuspecting human doesn't wander into the robot's work area
and be injured. After installation, the robot manufacturer usually
provides operation and maintenance training to the customer.

Quality Control

Testing consists of two parts: functional accuracy and a process known as
"burn-in." Once the assembled robot is energized with power,
a computer program instructs the controller to move the robot arm through
a
series of motions. Accurate recordings of these motions are made, any
problems corrected. Then the robot is placed into operation continuously
for several hours. This is called burn-in, and it serves two functions.
First, any loss of accuracy can be detected using the data from the
functional test. Such an instance would indicate a design problem, loose
assembly, defective bearing, or the like. Second, the trial run brings the
electronics and hydraulics up to operating temperature. This is important
because the controller is programmed with correction factors called
offsets. These offsets compensate the feedback from the position sensors
to allow for temperature variation of the components. With the machine
warmed up, the programmer can place the correction factors into the
program to provide optimum performance.

The Future

Robotics is one of the fastest growing segments of the industrial machine
market. Driven mainly by advances in computer technology, older robots are
quickly made obsolete by new models. Japanese firms are leading the
development of robotics, and many of their designs incorporate the new
science of artificial intelligence which allows robots to
"learn" and "adapt" their operations on their
own.

Advances in cameras and electronic vision will also impact the robot in
the 1990s. Many robots will enter new areas of use such as medical and
food service, which will bring more people into contact with them than
previously occurred in the industrial workplace.

Where To Learn More

Books

Berger, Fredericka.
Robots: What They Are, What They Do.
Greenwillow Books, 1992.

Ulrich, Robert A.
The Robotics Primer: The What, Why, and How of Robots in the
Workplace.
Prentice-Hall, 1983.

User Contributions:

Ã˜ Identifying skill levels of operators, Multi skilling of operators through proper training, delegating area ownership in their respective areas.
Ã˜ Active involvement of all operators for improving resource utilization, motivating team for suggestions and kaizen approach

Just to say that hydralics have not been used to power robots for several years now. Gas springs are sometimes used to balance a robots mechanical system but motive force is supplied by brushless AC servomotors in almost every robot. Robots are also not reliant on heavy bases to keep them stable - they are bolted to the floor, wall, or gantry, often via a baseplate, raft or other metalwork. Otherwise nice piece.